<!DOCTYPE html>
<html>
<head>
  <style type="text/css">
    .box {
      height: 30px;
      width: 200px;
      background-image: linear-gradient(black, black);
      border-radius: 25px;
      border: 1px solid green;
    }
  </style>
</head>
    <script>
        window.onload = function() {
            if (window.testRunner) {
                testRunner.waitUntilDone();
                testRunner.setBackingScaleFactor(2, finishTest);
            }
        }

        function finishTest() {
            setTimeout(function() { testRunner.notifyDone(); }, 0);
        }
    </script>
<body>
  <!-- You should see no red leaking through the inner edge of the border. -->
  <div style="background-color: red; padding: 10px; width: 200px">
    <div class="box"></div>
  </div>
</body>
</html>
